The present disclosure is directed to an air purification apparatus and more particularly to a particle made in a special fashion as discussed below capable of removing volatile organic compounds from the air, and is further capable of subsequent regeneration and repetitive recycling. The present apparatus is directed to a particle which is primarily particulate divinylbenzene (DVB hereinafter). In the preferred form, substantially pure DVB is formed into particles providing a fairly large surface area, upward of 750 or 800 m.sup.2 /g and has a pore volume in the range of about 2.24 cc/g. It tolerates an upper operating temperature above 250.degree. C. even as much as 290.degree. C. It is structurally stable notwithstanding the fact that it is in excess of 70% pores and yet is able to be regenerated on exposure to heated fluids which remove the adsorbed materials. Heated fluids such as N.sub.2, CO.sub.2, and the like can be used to purge adsorbed volatile organic compounds (VOC hereinafter). To obtain these benefits, beads of DVB are made and screened to select beads having a size able to pass through the range of screens of about 20 to about 50 mesh. The beads are preferable spherical. They are typically only about 30% or slightly less in material and the remainder of the bead is pores or cavities within the spherical bead.
Known references having a bearing on the present disclosure include U.S. Pat. No. 3,727,379 which is directed to a polymer system including DVB and styrene and which yields a surface area which is markedly lower, typically about 100 m.sup.2 /g and which has a very low pore volume, perhaps only one-sixth or one-eighth of the pore volume of the present disclosure. That disclosure sets out a pore volume of 0.3 cc/g. That disclosure has a limited operating temperature range not listed specifically, but which is inferentially markedly less than the temperature range permitted in operation by the present apparatus. It is noted that the styrene constitutes 20% to 98% of the material of that disclosure. Another reference is U.S. Pat. No. 4,239,508 which is a cumene adsorbent material of DVB, ethylvinylbenzene, styrene or mixtures thereof. The '508 disclosure is substantially silent as to details of the particles. For instance, it is not recited whether or not the material in that reference is porous, and if it has pores, pore size is not given. It is merely described as a cumene adsorbent material.
The present disclosure is believed to be an unobvious advance over the materials of the two references, and is further able to be used in a high temperature regeneration system for the DVB material for purification of VOCs. Advantages and benefits of the present material and the method of use thereof are set forth below.
This disclosure is directed to a DVB material useful in vapor recovery. It is particularly useful in removing VOCs from air or other atmospheres. Examples of such materials include gasoline, benzene, typical chlorinated solvents, various alcohols, esters, acid gases and the like. In the preferred form, the present material is substantially pure DVB. By this term, references made to DVB beads which has been processed at the time of manufacture and is intended to be substantially free of trace constituents. In fairness to the process of manufacturing, there may be traces of catalyst in the material, but for all practical purposes, such foreign constituents are substantially nil. Moreover, the present disclosure is directed to a DVB which is in particle form, typically passing through screens of about 20 mesh to about 50 mesh, U.S. standard. The beads are generally spherical and are substantially open cavities or pores. The beads are in the range of about 30% material and 70% pore, the maximum being about 72% or even 75% pores. The remainder of the material is DVB. It is desirable that the product have a pore volume of at least 1.8 cc/g typically up to about 2.4 cc/g. The preferred embodiment is around 2.24 cc/g. The pores are as small as 0.04 microns; indeed defining a typical pore size at that diameter suggests that there will be number of pores which are somewhat smaller as well as those which are larger.
The unobvious bead of the present disclosure is generally inert, generally spherical, and provides a maximum surface area in the range of about 700, and as much as 800 m.sup.2 /g. This surface area partially defines the aforementioned pore volume of up to about 2.4 cc/g for the product. Moreover, it is made to withstand an actual operating temperature of 290.degree. C.; that is, it can be exposed to a purging step in which purging material is flowed in, through and around a bed of such beads to remove adsorbed materials. At a few degrees above this upper cut off temperature, the beads become tacky and will ultimately melt. When tacky, they may well loose their desired spherical shape, and deformation may also change the density of the product. The round beads (up to about 28% solid material and 72% pores) yields beads in quantity having a collective density described below.
The beads (in response to testing for physical characteristics) range from a large pore diameter of about 242 angstroms to a median pore diameter of about 55 angstroms, with a number of pores as low as 40 angstroms. This yields an apparent density of 0.331 g/mL. Approximately two thirds of the pores lie in the range of about 30 to 95 angstroms diameter. The remaining one third is outside this range and is typically distributed toward the larger pores, not toward the smaller end of that range.